1. Field of Invention
This invention relates to tension leg platforms (TLP) and, in particular, to releasable connectors for securing the strings of tendon segments to anchor templates located at the seabed.
2. Prior Art
FIG. 1 herein, the U.S. Pat. Nos. 4,391,554 to Jones, and 4,439,055 to Quigg, et al.
FIG. 1 illustrates a tension leg platform outer column (jacket) C, typically located at each corner of a platform, with tendons T maintained continuously in tension, using platform buoyancy, with an anchor template AT at the seabed. The anchor template AT is secured to driven and/or drilled and cemented piles P. Although only one string or leg of tendon segments, coupled together, is shown, several such strings may run from various anchor templates to the platform, for the purpose of mooring the TLP to the seafloor.
The lower connection of the string of tendon segments is made by a latch and flex joint bottom or anchor connector AC, guided into the template receptacle R by a guide cone GC during installation, and latched to the template receptacle. Bending moment, caused by lateral motions of the TLP, is reduced by the flexible joint of the bottom connector AC. Such a lower anchor connector is shown in the Quigg, et al, patent, supra.
At the upper end of the string of tendon segments, there is provided a top connector for connection to the outer column C, not shown.
As shown in FIG. 1, the tension leg platform tendon system may extend through a hawsepipe HP and above the water level WL so that the bore of the tendon segments is accessible above the water. This type of TLP typically would include a bearing B at the lower end of the hawsepipe, to react lateral loads and motions into the tendon. Such a bearing is described in the Jones patent, supra, also having a flexible joint arrangement to minimize bending loads into the tendon. Such a tension leg platform tendon system has the advantage, among other things, of allowing tools to be conveniently lowered through the tendon segment bores by which the tendons can be inspected, and by which the lower connector may be disconnected from the anchor template AT so that the platform may be moved, when and if desired. Such a tool for disconnecting the bottom connector is shown in the Quigg, et al, patent, supra.
Another type of tendon system for connecting a tension leg platform is one which is suspended from outside the tension leg platform and below the waterline, rather than run through hawsepipes as above described, shown in FIG. 2. With this type of tendon system the release mechanism for disconnecting the bottom connector of the above described system may be used, but access to the tendon bore may be inconvenient, making an anchor connector which is releasable from outside the tendon desirable. Also, sometimes the inner bore of the tendons may become clogged with debris, or perhaps it might be desirable to have baffles within the tendons, making internal access impossible.
In each of the above cases, a primary release mechanism that is self-actuating, i.e., operable without the use of tools, without the use of a remote operable vehicle (ROV) and/or a release mechanism that is operable by a tool outside the tendons would obviously be preferred.
It is, therefore, an object of this invention to provide such a self-connecting bottom connector with a self-actuating release mechanism as a primary means of disconnecting the bottom connector, i.e., one which is releasable without the use of tools, without a remotely operable vehicle (ROV) intervention or any other external intervention.
It is also an object of this invention to provide a self-connecting bottom tendon connector for connecting the tendons of a tension leg platform which may be conveniently connected and disconnected without tools insertable through the inner bore of the tendons.
It is still another object of this invention to provide such a self-connecting bottom connector with a releasable means which is fail-safe and which can provide long life and minimize installation and removal requirements.
Still another object of the invention is to provide such a bottom connector with a redundant means for releasing the bottom connector, if desired, in the event the primary means of disconnecting the bottom connector is not used for whatever reason.